Ensuring correct values for &SIZE and &MAXSIZE

If you allocate a data set using the TSO/E ALLOCATE command and you do not explicitly specify space requirements, then &SIZE and &MAXSIZE do not contain the correct values. Instead they both contain a value of zero. If your ACS routines rely on the values of &SIZE or &MAXSIZE in this situation, the data set might be assigned to the wrong class or group.

For a VSAM data set definition, the &SIZE and &MAXSIZE read-only variables reflect the space value specified in the CLUSTER component. If one is not specified in the CLUSTER component, then the space value specified in the DATA component is used. If a space value also is specified for the INDEX component and it is of the same type of space unit; for example, both are in tracks, cylinders, KB or MB, it is added to what was specified for the DATA component. If the INDEX component space unit is not of the same type as specified for the DATA component, it is ignored and not added to &SIZE or &MAXSIZE. For DFSORT work data sets, &SIZE and &MAXSIZE are zero. In the RECALL environment, &SIZE and &MAXSIZE are zero for empty partitioned data set and PS data sets because the size of the existing data set is not known at the time that DFSMS runs its ACS routines.

As input to data class ACS routine, &SIZE and &MAXSIZE are calculated from space information from JCL or IDCAMS, as follows:

For non-VSAM data sets:
- &SIZE = P + Directory (if any).
- &MAXSIZE = P + (S*15) + Directory (if any).
For VSAM data sets:
- &SIZE = P.
- &MAXSIZE = P + (S*254).

After data class is derived by the data class ACS routine, &SIZE and &MAXSIZE are recalculated depending on whether Extent Constraint Removal is specified or not in the selected data class before calling subsequent data class routines, as follows:

For non-VSAM data sets, if no space is specified on JCL, then the space values defined in the selected data class are used to recalculate &SIZE and &MAXSIZE as follows:
- &SIZE = P + Directory (if any).
- &MAXSIZE = P + (S*15) + Directory (if any).
For VSAM data sets, regardless whether space is specified or not, &MAXSIZE is recalculated depending on the specification of Extent Constraint Removal attribute as follows:
- If Extent Constraint Removal = NO, then &MAXSIZE = P + (S*122)*volcnt.
- If Extent Constraint Removal = YES, and the ADD' '1 Volume Amount in Data Class = P, then &MAXSIZE = ((P+S*122))*volcnt.
- If Extent Constraint Removal = YES, and the ADD' '1 Volume Amount in Data Class = S, then &MAXSIZE = ((P+S*122)) + ((S*123)*(volcnt-1)).